1. Field of the Invention
The present invention generally relates to the interconnection of optical fibers, and more particularly to a method and apparatus for simultaneously cleaving the terminal ends of a plurality of optical fibers, and imparting an oblique angled finish to the terminal ends.
2. Description of the Prior Art
In recent years, fiber optic cables have replaced traditional copper wire as the preferred medium for telecommunications. As with copper wires, it is necessary to provide cross-connections and interconnections between optical fibers at various locations in the distribution system. This is typically accomplished with the use of an optical fiber connector or splice, but it is first necessary to prepare the terminal ends of the fibers being spliced. The prior art techniques for fiber preparation include cleaving the end of the fiber to provide a planar finish perpendicular to the fiber axis, which minimizes insertion losses associated with irregularities on the fiber end face. Early prior art cleaving devices were designed to cleave a single (discrete) fiber; later devices allow for the simultaneous cleaving of multiple fibers, for example, fibers which have been formed into a fiber ribbon. One such exemplary prior art cleaving device 1 is shown in FIG. 1, and is described in further detail in U.S. Pat. No. 5,024,363.
The prior art multi-fiber cleaver 1 is generally comprised of a base 2 having a support surface 3 for receiving the fibers, and a scribing wheel 4 which moves transversely with respect to the fiber axes. Support surface 3 includes a guide ramp 5 for receiving a fiber holder, and a pair of clamping pads 6. Pads 6 are aligned with another pair of pads 7 on a lid or clamp cover 8 which is hinged to an edge of support surface 3. The fibers to be cleaved are set on support surface 3, with their terminal ends overlying pads 6; the fibers are securely held in place between pads 6 and 7 when cover 8 is pushed against surface 3. Then, as scribing wheel 4 slides transversly along base 2, it produces a score line on each of the fibers. The cleaving operation is completed by pivoting an arm 9 downward, causing a pushing member or anvil 10 at the end of arm 9 to break the fibers at the score lines.
The prior art cleaver 1 simplifies the cleaving operation by making it possible to simultaneously cleave all of the fibers at once, and also ensures that each of the fibers is cleaved at the same relative location, i.e., the terminal portions of the fibers have the same length. It may be noted that this cleaver may be used for both fusion splicing and mechanical splicing. Fiber length is particularly important in both fusion and mechanical splices since the cleave length must be exact to avoid any offset of the fiber end faces, which would be detrimental to splice performance.
The prior art further recognizes that signal transmission may be improved by imparting an angled finish to the end face of the fibers. This construction results in reduced internal reflections of the signals at the end face. See, e.g., U.S. Pat. Nos. 4,615,581, 4,695,126, 4,978,193, 5,062,682 and 5,140,660. While each of these patents describes a ferrule-type connector, the same principle (minimizing reflections with an angled end face) equally applies to mechanical, butt-end splices. The prior art includes appropriate techniques for imparting an angle cleave to the end face. For example, U.S. Pat. No. 5,048,908 illustrates a technique which requires that the fiber be placed under a torsional load; this technique is shown in FIG. 2. This prior art cleaving device 11 also has a base 12, lower clamping pads 13, upper clamping pads 14 and a scribing wheel or other cutting tool 15. Additionally, cleaver 11 includes a fiber holder or collet 16 which is rotatably supported, whereby collet 16 may be rotated and, consequently, the terminal end of the fiber is twisted. When a torque is so applied to the end of the fiber prior to the scoring operation, an angled end face results.
One problem that remains unsolved in this area is the cleaving of multiple fibers, such as are in a fiber ribbon, to impart an angle cleave on each of the fiber end faces. It is rather tedious, if not practically impossible, to use the technique of the '908 patent on each individual fiber in a ribbon, since this would require that the collet be successively placed about, and then removed from, each fiber; this also requires excessive manipulation of the ribbon which can lead to damaging one or more of the fibers. If any fiber in a ribbon becomes so damaged, or if any single fiber is not properly cleaved on the first try, then it may become necessary to re-cleave all of the fibers. This is due to the above-mentioned requirement that all of the fibers have the same predetermined length. It would, therefore, be desirable and advantageous to devise a cleaver similar to that of the '363 patent, which may simultaneously cleave a plurality of fibers, but which imparts an angle cleave to each of the fiber end faces. Unfortunately, it has heretofore been impossible or impractical to combine the teachings of the '363 and '908 patents. For example, it is not possible to simply use a single collet which would be simultaneously attached to the ends of all of the fibers. This configuration would tend to make the entire ribbon twist, as opposed to any individual fiber; it would also be rendered ineffective by the clamping of the fibers between the pads. Conversely, if the pads were removed or loosened, then twisting of the ribbon with a collet would cause some of the fibers to move away from the plane formed by the pads, and so the scribing wheel could not make a score line on each of the fibers in a single motion. Another combination of these techniques would require a plurality of collets, each being attached to one of the fibers in the ribbon after the ribbon has been secured to the cleaver. The fibers may be scored after each collet has been secured in a rotated position. It has, however, proven greatly impractical to provide suitable means to support such a configuration of collets (the close fiber spacing in a ribbon makes this even more difficult), and this technique would still require excessive manipulation of the fibers.